<?php
 class PHPExcel_CalcEngine_CyclicReferenceStack { private $_stack = array(); public function count() { return count($this->_stack); } public function push($value) { $this->_stack[] = $value; } public function pop() { return array_pop($this->_stack); } public function onStack($value) { return in_array($value, $this->_stack); } public function clear() { $this->_stack = array(); } public function showStack() { return $this->_stack; } } 